Circuit breaker having ambient temperature compensation



Sept. 20, 1966 A MAlER ET AL 3,274,357

CIRCUIT BREAKER HAVING AMBIENT TEMPERATURE COMPENSATION Filed Dec. 1, 1964 2 Sheets-$heet 1 t INVENTORSI fl/frea E M01?! ATTORNEY Sept. 20, 1966 A, E. MAlER ET AL 3,274,357

CIRCUIT BREAKER HAVING AMBIENT TEMPERATURE COMPENSATION Filed Dec. 1, 1964 2 Sheets-Sheet 2 INVENTORS Alfred 1 /Vfaz'er Henry 5. h/ingar MAM;

A TTORA/[V United States Patent 3,274,357 CIRCUIT BREAKER HAVING AMBIENT TEMPERATURE COMPENSATION Alfred E. Maier, Colonia, and Henry S. Wingard, Cranford, N..l., assignors to Federal Pacific Electric Company, a corporation of Delaware Filed Dec. 1, 1964, Ser. No. 415,117 9 Claims. (Cl. 200-416) This invention relates to circuit breakers and more particularly to molded case circuit breakers having trip mechanisms which employ a current responsive bimetallic member for effecting automatic operation of the breaker.

An object of this invention is to provide a circuit breaker having improved thermally-actuated overcurrent responsive characteristics which are substantially unaffected by variations in the ambient temperature of the environment in which the circuit breaker is found.

A further object of the invention is to provide a single point ambient temperature compensating means (for a multipole circuit breaker.

Still another object of this invention is to provide a circuit breaker equipped with a thermally responsive overcurrent responsive trip device with means for compensating the operating point of the breaker for changes in ambient temperature.

The .above and other objects and advantages of the invention will be readily apparent to those skilled in the art from the following detailed disclosure taken with an illustrative embodiment shown in the accompanying drawings. In those drawings:

FIG. 1 is a side view of a multipole circuit breaker embodying the invention partly in section as viewed from the plane 11 in FIG. 2;

FIG. 2 is a plan view of the circuit breaker of FIG. 1 with some parts broken away and other parts omitted;

FIG. 3 is a fragmentary cross-sectional view of the common trip bar taken along the plane 3--3 of FIG. 2;

FIG. 4 is a fragmentary cross-sectional view of the trip bar .and latch on an enlarged scale, as viewed from the plane 44 of FIG. 2 with some parts omitted and wit-h other parts broken away or in section in the interest of clarity; and

FIGS. 5 and 6 are fragmentary cross sectional views of the trip bar and latch on an enlarged scale according to FIG. 4 showing the change in relative position of the latch, the trip bar, and a current-carrying bimetal.

It will be understood that the invention described herein may be applied to any automatic electrical circuit breaker which employs a bimetallic element as a current responsive element for effecting automatic tripping and for purposes of illustration only it is shown herein as applied to a circuit breaker of the type described in Wingard Patent Application Serial No. 196,094 filed May 21, 1962, now U.S. Patent No. 3,209,098, which is assigned to the same assignee as the present invention.

Referring to the drawings, the circuit breaker mechanism is enclosed in a case of molded insulation including a cover 10 and a base 12. The circuit through an illustrative pole of the circuit breaker (when it is closed).

extends from one terminal 14 to the stationary contact 16 thence to movable contact 18, through the contact arm 20, along a conductive flexible braid 22 through bimetal 24 to conductive bar 26, and thence to the opposite terminal 28. Contact arm 20, which carries contact 18, is in turn carried by pivot 30 in the contact arm carrier 32 and is biased by compression springs 34 in a direction to build up contact pressure when the contacts are closed. When the contacts are open, the swing of the contact arm produced by the springs 34 is limited by the engagement of the portion 20a of the 3,274,357 Patented Sept. 20, 1966 contact arm with the bottom edge 32:: of the channeledshaped contact arm carrier 32. Contact arm carrier 32 is aiiixed to the insulated shaft 36 the ends of which are pivotally supported by corresponding bearing portions of the molded base 12. Plural contact arm carriers 32, with respective contact arms 20, are mounted on the aforesaid shaft for coordinated cooperation of the contacts of a multi-pole circuit breaker.

An over-centering spring mechanism indicated generally at 38 is provided for operating the contacts between closed and open positions and for effecting automatic release in opening of the contacts in response to an overload. The operating mechanism includes a manual operating lever 40 and a handle 42. Lever 40 is pivoted at its lower extremity in a fixed frame 44 secured to the breaker base 12. The frame includes a pair of spaced metal members or plates which extend from a point adjacent the midpoint of the breaker casing toward one end of the case. An overload release member or cradle" 46 has a pivot 48 fixed in the frame 44. A pair of toggle links 50, 52 are pivotally connected to each other at the knee 54. The toggle links have a top pivot 56 and a bottom pivot 58 in members 46 and 32 in the center pole of the illustrative breaker. Where there are plural contact carriers 32, for a corresponding number of poles, there is here (as is usual) only a single operating mechanism for all of the contact arm carriers operated by the square shaft 36. Two pairs of springs 60 extend between the manual lever 40 and the knee 54 of the toggle although only one pair is visible in FIG. 1.

The breaker operating mechanism 38 and a cooperating secondary latch 62 are located at the center pole position of the illustrated embodiment of the invention. The end 46a of the cradle 46 remote pivot 48 (FIG. 4) is normally restrained against movement in the togglecollapsing direction by the secondary latch 62. Secondary latch 62 has a back wall 64 which provides pivots 66 at two spaced points on the frame 44. A latch arm 68 extends at right angles to the back wall 64. An offset portion 70 of the latch wall 64 is engaged by end 46a of the cradle; the point of engagement between the cradle and the secondary latch is almost in line with the pivots 66 so as to produce a force having a minimal component tending to rot-ate the latch about its pivot. The maximum component of force is directed vertically (FIG. 4) through the pivots 66 and is taken up by the frame 44. A rearwardly extending projection or tail 72 depends from the latch wall 64 and cooperates with cradle end 46a during the latch-resetting operation. Latch stop 74 engages the frame 44 to limit the rotation of the secondary latch in the trip direction.

In FIGS. 2 and 3 the trip bar 76, of insulation, extends across all the pole positions and is pivoted at two points 78 on the frame 44. The ambient temperature compensator 80, which acts as a primary or main latch, is mounted on the trip bar between its pivots 78. The ambient compensator (FIG. 4) includes a pair of confronting substantially fiat bimetal members 82, 84 mounted at one end on opposite sides of the broad face of the trip bar 76, by rivets 86, with their free ends extending in the same direction. Bimetal deflection sensitivity is a function, in part, of the thickness of the bimetal material. The thinner the bimetal the greater the sensitivity. The compensating bimetals are short, compared to bimetal 24, and must have a higher deflection sensitivity in order to compensate properly for changes in ambient temperature. The bimetals 82, 84 of the compensator, which are thinner than the overcurrent sensing bimetal 24, are interposed between the bimetal 24 and the secondary latch 62 and must transmit the force required to overcome latch friction with a minimum of mechanically produced deformation which would change the calibration of the breaker. The bimetals 82, 84 are aligned and are similarly oriented, with their high expansion side to the right as viewed in FIG. 4, so that change in ambient temperature will cause the free end of both bimetals to .deflect in the same direction. A latch member 88, which is wider than the thickness of the narrow face of the trip bar 76, is positioned between the free ends of the bimetals 82, 84, adjacent the trip bar and is retained therebetween by interengagement of projections 89 on the latch member with like notches 90 in the bimetals .82, 84. It will be appreciated that, were the upper ends of bimetals 82 and 84 united by rivets there would be a kind of restraint that would interfere with their sensitive response to ambient temperature changes. Part 88 couples the bimetals 82 and 84 together in a manner to exert constraint only transverse to the broad faces of the confronting bimetals. The bimetals 82, 84 are free to move, lengthwise, with respect to one another. One end of the latch member 88 having specially prepared surfaces 88a, 88b, to be discussed in detail below, extends beyond the lateral edge of bimetals 82, 84 for engagement by the secondary latch 62. The aforementioned interengagement between the latch member and the bimetals prevents any lateral, longitudinal or vertical displacement of the latch member 88 relative to the bimetals but only provides transverse constraint to the bimetals. The transverse restraint couples the bimetals 82, 84 and gives the compensator suflicient stiffness to avoid the unwanted deformation yet allows the use of relatively thin, sensitive, bimetals 82, 84. When the bimetals deflect due to change in ambient temperature, a slight amount of rocking movement between the latch member and the bimetals is possible allowing the latch member to remain in position without tilting appreciably, thus preserving the angular relationship between the latch member and the secondary latch. The bimetals 82, 84 are initially parallel to the planes of the broad faces of the trip bar 76 after being riveted thereto but when the latch member 88 is inserted between the free ends of the bimetals they are forced away from one another against their inherent resilience or springiness so as to securely locate the latch member 88 therebetween. All parts of bimetals 82 and 84 (except for the secured ends) are spaced from trip bar 76 so as to provide clearance for temperature responsive movement, and this clearance is preserved throughout the range of ambient temperatures for which compensation is desired. The initial bias produced by inserting the latch member between the ends of the theretofore flat bimetals 82, 84 insures that the temperature produced deflection of either of the bimetals will be reflected in movement of the trip bar without lost motion and also insures that when the trip bar 76 is driven by the current carrying bimetal both of the compensating bimetals will participate in the releasing operation. The bimetals 82, 84 may be considered end loaded columns since the latch force is applied to latch member 88 and, even though thin, are able to withstand the pressure exerted by the secondary latch 62.

Bimetals 82, 84 are identical and are both provided with a clearance aperture 91 through which extends the calibrating screw 92 that is threaded through the trip bar in registry with the bimetal 24 at the center pole. Similar calibrating screws 92 are provided for the outboard poles (FIG. 3) for engagement by respective bimetals 24. Spring 94 is tensioned between a stud 95 on the trip bar 76 and the latch 62 and urges them into engagement as shown in FIG. 4. Spring 94 engages the trip bar 76 at a point adjacent to and slightly above its pivotal axis (78, 78a) to provide counterclockwise bias. Clearance notch 96, for the spring 94, is provided in both of the compensating bimetals although only visible in bimetal 82 in FIG. 3. Spring 94 engages the latch wall 64 at a point spaced above the latch pivotal axis (66, 66) to bias the latch 62 clockwise toward the latch member 88.

Referring to FIGS. 2 and 4, the secondary latch arm 68 has a heat-treated, hardened flat-surface right-angle portion 98 which has been shaved to a flat surface for accurately engaging the upper surface 88a and end 8812 of the relatively stiff metal latch member 88. Surface 88a is a smooth rolled surface to reduce the latch friction, and edge 88]) is burr-free, having been sheared downward. In this construction it is possible to use, as a part of the ambient compensator means 80, a heat treated latch member 88 which is hardened so as to minimize wear incident to operation of the circuit breaker and thus preserve the calibration of the breaker. The amount of latch engagement is determined by the configuration of the hardened accurately machined confronting parts. In the embodiment shown in the drawings the burr-free end 88b of the latch member engages the vertical surface of the latch arm to accurately limit their inward movement toward one another. The point of engagement of the secondary latch arm 68 and the member 88, forming part of the ambient temperature compensator 80, is a reaction point for the previously described small component of force exerted by the cradle end 46a which tends to rotate the secondary latch 62 about its pivotal axis 66, 66, as viewed in FIG. 4. The configuration of the ambient temperature compensator is such that the force on the member 88 is in a vertical plane close to the trip bar pivots '78, 78 and to the left of the pivot as viewed in FIG. 4. The selected configuration produces a small counterclockwise movement that biases the trip bar 76 toward the secondary latch. The forces thus produced are minimized.

The relative location of the pivots of the trip bar 76 that carries the main latch or ambient compensator 80 and the secondary latch 62 are fixed by the pivots of those parts in the frame 44. The pivot friction of the trip bar in the frame 44 is minimized by the use of grommets which engage ears 102 on the trip bar 76 and appropriate apertures that are formed in the frame 44.

Each of the poles is provided with an overcurrent sensing means in the forms of the main current-carrying bimetal 24. The use of the bimetal 24 is desirable since it provides an inverse time characteristic so that as the overload current increases the time of response is decreased. Circuit breakers are normally calibrated at a nominal ambient temperature of 25 C., after having been allowed to reach equilibrium, by setting the gap between the end of the calibrating screw 92 and the bimetal 24 for each pole. The separation between the active end of the main bimetal 24 and the end 92a of the calibrating screw determines the amount of deflection of the bimetal that must occur before the breaker is tripped by the release of the secondary latch and the subsequent release of the cradle 46. The high expansion side of bimetal 24 is to the left in FIG. 4 and when bimetal 24 deflects, due to heat produced by the current flow therethrough it deflects toward the end 92a of the adjustment or calibrating screw 92 carried by the trip bar 76. If the temperature of the bimetal continues to increase, it drives the trip bar 76 clockwise, to disengage the secondary latch 62 from the latch member 88 and open the breaker. The bimetal 24 is, by its nature, responsive to temperature change both that caused by the current it carries and the ambient temperature to which it is exposed. While in the illustrative embodiment of the invention shown in the drawings the operative temperature change is produced by the load current flowing through the bimetal an indirectly heated bimetal may also be used. The heat due to current flow will change the temperature of the bimetal 24 and cause the free end to move. Since bimetal 24 is temperature responsive, when the ambient temperature to which it is exposed is raised above the calibration temperature, the higher temperature will cause it to deflect toward the trip position as if an additional current were heating the bimetal. Without ambient temperature compensation the gap between the calibrating screw 92 and the bimetal 24 would be reduced and the breaker will tend to trip out prematurely, i.e., at a lower actual current value. Conversely if the ambient temperature at which the breaker is operated is lower than 25 C. then a greater amount of heat must be generated by the current flowing in the bimetal so that higher currents than desired flow through the breaker before it trips. The foregoing problems are obviated by the employment of the ambient temperature compensating means shown and described herein.

Ambient temperature compensating means used heretofore have been relatively complex in some instances requiring special treatment of the compensating bimetal in an attempt to provide a long-wearing, hard, smooth surface for engagement by the latch. Also, many proposed compensating devices have lacked a requisite degree of sensitivity to provide adequate ambient compensation or suificient stiffness to transmit the force required to overcome the latch friction. Referring to FIGS. 4, 5 and 6, the mode of operation of the ambient compensating means 80 is illustrated in detail. FIG. 4 is illustrative of the relative position of the bimetal 24 and the calibrating screw 92 at a calibration temperature of 25 C. The gap between the end 92a of the screw and the bimetal is determinative of the level of current flow through the bimetal that would be required for currentdependent tripping. When the ambient temperature in- .creases, the bimetal 24 has a tendency to move toward the calibrating screw from its initial position (shown in phantom) to the position shown by solid lines in FIG. 5 as if in response to the flow of additional current. If no provision were made for compensating for this increase in deflection not due to current it can be seen that the amount of current-generated heat required would be smaller and that the breaker would therefore trip at lower current values than desired. FIG. 5 illustrates a change in ambient temperature not due to current produced heating. It will be seen that the gap between the screw and the bimetal has been maintained substantially constant. This is due to the response of the bimetals 82, 84 which form part of the compensator 80. Bimetals 82, 84 are also affected by the change in ambient temperature and tend to deflect in a direction opposite to that of the main bimetal 24 because of their orientation. They are secured at one end to the trip bar 76 and are restrained at the other end against movement relative to the latch 62 by the engagement of latch member 88 with the face 98 of the latch arm 68. The trip bar to which they are secured is pivotally mounted and free to rotate, against the bias of spring 94, and therefore, as they deflect the trip bar 76 is caused to change its position. Since the bimetals are maintained in tight engagement with the latch member 88, both must concurrently deflect the same amount before the trip bar rotates. The deflection vs. temperature characteristics of the bimetals 82, 84 are chosen so that they will match the ambient temperature produced change in position of the main bimetal 24 with a similar, substantially equal, change in the position of the calibrating screw 92 carried by the trip bar when 100% compensation is intended. Compensation of a lower extent, e.g., 80%, is also used in the art. Accordingly, the term compensation is intended to include both full (100%) or partial (less than 100%) compensation. If the deflection of the bimetal 24 is due to heat generated by current flow, then the trip bar does not move and screw 92 remains in its fixed position while the bimetal 24 advances toward the trip bar. However, if the deflection is due in part to change in the ambient temperature, then the trip bar is moved by the bimetals 82, 84 and screw 92 also moves in the same direction as the bimetal 24 thereby compensating for the ambient temperature produced deflection, that is, bimetals 82, 84 only compensate for a change in position of the main bimetal 24 due to a change in ambient temperature. In this movement the latch member 88 remains in virtually the same plane so as to not cause any significant change in its positon relative to the secondary latch arm thereby avoiding a change in latch engagement and latch force. In FIG. 6 the low ambient temperature position of the trip bar is shown. In this view the bimetal 24 is shown withdrawn from its initial position, shown in phantom, due to a lower ambient temperature and the calibrating screw 92 is shown advanced toward the new position of the main bimetal 24 by virtue of the pivoting trip bar 76, under the .bias of spring 94, due to the deflection of the compensating bimetals 82, 84.

The latch friction between the parts 88 and 98, and the bias of spring 94 must be overcome by the bimetal 24 through the interposed compensator 80. The use of paired or con-fronting bimetals 82, 84 provides a compensator which has suflicient stiffness to transmit the tripping force generated by the current responsive bimetals 24. The passage of current above the desired value through any bimetal 24 heats the bimetal and it deflects. The bimetal 24 pushes against the calibrating screw 92 to pivot the trip bar to cause the latch which then causes the circuit breaker to open. Circuit breakers employing the described ambient temperature compensatory means have successfully been tested over a temperature range from minus 40 C. to plus 60 C., with the trip current not varying beyond 95 to 104 p'ercent of nominal trip rating.

While the presently preferred embodiment of the invention has been shown and described those skilled in the art will realize that certain modifications and variations may be made therein without departing from the spirit and scope of the invention.

I claim:

1. A circuit breaker having a pair of separable contacts, operating means for opening and closing said contacts, said operating means including a releasable member, means releasable restraining said releasable member,

and a current responsive bimetal for causing said restraining means to effect automatic opening of the contacts by said operating means in response to an overcurrent, said releasable restraining means including a trip member, a pair of ambient temperature responsive bimetals having confronting secured ends fixed to said trip member and having confronting movable ends, said movable ends having means providing only transverse constraint therebetween, said trip member and said temperature compensating bimetals constituting means for transmitting tripping forces applied by said current responsive bimetal in the direction to release said releasable member, said ambient temperature compensating bimetals being mounted to deflect in the same direction as one another and being disposed to provide compensation for the effects on said current-responsive bimetal produced by ambient temperature changes.

2. A circuit breaker according to claim 1 wherein said ambient temperature responsive bimetals are mounted on opposite faces of said trip member but spaced therefrom except at the secured ends thereof, throughout the operative range of ambient temperature compensation.

3. A circuit breaker according to claim 1 wherein said means providing transverse constraint includes a latch portion for engagement by said releasable member.

4. A circuit breaker in accordance Wit-l1 claim 1 wherein each of said compensating bimetals exerts spring bias against said transverse constraint providing means which bias opposes the spring bias of the other of said pair of compensating bimetals which thereby promotes participation of both of said compensating bimetals to transmitting circuit breaker releasing force from said current responsive bimetal.

5. A circuit breaker having a pair of separable contacts, operating means for opening and closing said contacts, said operating means including a releasable member, means releasably restraining said releasable member, and a current-responsive bimetal for causing said restraining means to effect automatic opening of the contacts by said operating means in response to an overcurrent, said releasable restraining means including a trip member, a pair of ambient temperature responsive bi metals having confronting secured ends fixed to said trip member and having confronting movable ends, a latch part normally restraining said releasable member and providing only transverse constraint between the movable ends of said compensating bimetals, said ourrent-responsive bimetal being arranged to operate said trip member in the direction to free said releasable member from restraint by said latch part, said ambient temperature compensating bimetals being arranged to deflect in response to temperature changes in the opposite direction to said current-responsive bimetal and being mounted to provide compensation for the effects on said current-responsive bimetal produced by ambient temperature changes.

6. A circuit breaker in accordance with claim 5, wherein said movable ends of the compensating bimetals are spaced apart by said latch part and wherein the latter is separate from and angularly movable relative to said compensating bimetals so that change in angular disposition of said compensating bimetals resulting from ambient temperature change does not cause like angular change in the attitude of the latch part relative to the releasable member.

7. A multipole circuit breaker having a pair of separable contacts per mole, operating means for opening and closing said contacts conjointly, said operating means including a releasable member, means releasably restraining said releasable member, said releasable restraining means including a trip member extending across all of said poles, and a current responsive bimetal in each of said poles for causing said restraining means to effect automatic opening of the contacts by said operating means in response to an overcurrent in any of said poles, a pair of ambient temperature responsive bimetals having confronting secured ends fixed to said trip member and having confronting movable ends, said movable ends having means providing only transverse constraint therebetween, said trip member and said ambient temperature compensating bimetals constituting means for transmitting tripping forces applied by any of said current responsive bimetals in the direction to release said releasable member, said ambient temperature compensating bimetals being arranged to deflect in response to temperature changes in the opposite direction to said current-responsive bimetal and being disposed to provide compensation for the effects on said current-responsive bimetals produced by ambient temperature changes.

8. A circuit breaker having a pair of separable contacts, operating means for opening and closing said contacts, said operating means including a releasable memher means releasably restraining said releasable member, and a current responsive bimetal for causing said restraining means to elfect automatic opening of the contacts by said operating means in response to an overcurrent, said releasable restraining means including a trip member, ambient temperature compensating means including a pair of mutually confronting ambient temperature responsive bimetals, said bimetals each being secured at one end on respective opposed faces of said trip member, a latching member supported by said bimetals in spaced relation to said trip member, said latching member coupling said compensaitng bimetals and providing only transverse constraint thereto, said latching member having a latch surface engageable by said releasable member, said latch surface having a given angular relationship to said releasable member when engaged therewith, said trip member being pivotally movable by said compensating means to provide ambient temperature compensation while said angular relationship is maintained substantially constant.

9. A multipole circuit breaker having a pair of separable contacts per pole, common operating means for opening and closing said contacts conjointly, said operating means including a releasable member and latch means for releasably restraining said releasable member, current responsive means including a trip member extending across all of the poles for causing automatic opening of all of the contacts in response to an overload in any one pole, a current responsive bimetal in each pole, said bimetal being fixed at one end and adapted to engage said trip member at the other end for effecting automatic opening of the contacts in response to overload currents, ambient temperature compensating means mounted on said trip member, said compensating means including a latch portion for engagement by said latch means and a pair of compensating bimetals each secured at one end to opposite faces of said trip member and projecting therefrom in the same direction, said latching portion being disposed between the free ends of said compensating bimetals and biasing them apart.

References Cited by the Examiner UNITED STATES PATENTS 1,899,558 2/1933 Cohn et al. 200-113 2,162,521 6/1939 Armstrong 200-116 2,180,421 11/1939 Leonard 200-116 2,318,279 5/ 1943 Aschwanden 200-416 2,501,363 3/1950 Toth et al 200-116 2,693,515 11/1954 Hodnette et al 2001 16 2,769,938 11/ 1956 Pauly 2001 14 2,889,428 6/1959 Kingdon et a1 200-88 X 3,209,098 9/1965 Wiugard ZOO-88 BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

1. A CIRCUIT BREAKER HAVING A PAIR OF SEPARABLE CONTACTS, OPERATING MEANS FOR OPENING AND CLOSING SAID CONTACTS, SAID OPERATING MEANS INCLUDING A RELEASABLE MEMBER, MEANS RELEASABLE RESTRAINING SAID RELEASABLE MEMBER, AND A CURRENT RESPONSIVE BIMETAL FOR CAUSING SAID RESTRAINING MEANS TO EFFECT AUTOMATIC OPENING OF THE CONTACTS BY SAID OPERATING MEANS IN REPSONSE TO AN OVERCURRENT, SAID RELEASABLE RESTRAINING MEANS INCLUDING A TRIP MEMBER, A PAIR OF AMBIENT TEMPERATURE RESPONSIVE BIMETALS HAVING CONFRONTING SECURED ENDS FIXED TO SAID TRIP MEMBER AND HAVING CONFRONTING MOVABLE ENDS, SAID MOVABLE ENDS HAVING MEANS PROVIDING ONLY TRANSVERSE CONSTRAINT THEREBETWEEN, SAID TRIP MEMBER AND SAID TEMPERATURE COMPENSATING BIMETALS CONSTITUTING MEANS FOR TRANSMITTING TRIPPING FORCES APPLIED BY SAID CURRENT RESPONSIVE BIMETAL IN THE DIRECTION TO RELEASE SAID RELEASABLE MEMBER, SAID AMBIENT TEMPERATURE COMPENSATING BIMETALS BEING MOUNTED TO DEFLECT IN THE SAME DIRECTION AS ONE ANOTHER AND BEING DISPOSED TO PROVIDE COMPENSATION FOR THE EFFECTS ON SAID CURRENT-RESPONSIVE BIMETAL PRODUCED BY AMBIENT TEMPERATURE CHANGES. 